There's actually a tiny transformer and even tinier capacitors and inductors in these phone power supplies. The transformer is super-important, because it isola

There's actually a tiny transformer and even tinier capacitors and inductors in these phone power supplies. The transformer is super-important, because it isolates the AC line from the output, which is necessary so you don't electrocute yourself on the power supply. AC switching power supplies from tiny cell-phone chargers to big computer supplies are split by the transformer into a primary-side connected to the line, and a secondary side connected to the output. For safety and by law, there can't be any direct electrical connection between the primary and secondary side, so even the voltage feedback control signals need to be isolated with small transformers or optoisolators. And even any circuit board traces between the sides are required to be separated by a couple millimeters. P.S. Thanks everyone for the comments on my article.